On marking a letter or a symbol on a surface of a resin molded article, a composite material, or the like, there have hitherto been adopted spraying of inks by an inkjet system, screen printing, ink writing system, and so on. However, these methods involved problems, such as peeling of an ink surface, discoloration of inks, wear of an ink surface, etc. In order to solve these problems, in recent years, laser marking that is of a non-contact type and which has a fast marking speed and is easy in automatization and process management is adopted.
For example, PTL 1 describes a resin composition for laser processing comprising 100 parts by mass of a resin and 0.001 parts by mass or more and 20 parts by mass or less of a carbonaceous filler having a tint strength according to JIS K6217 of 50% or less. When the foregoing resin composition for laser processing is used, the laser absorbability is excellent, and the blackening or darkening of color of a base is inhibited. Thus, by adding coloring materials of various color tones, it is possible to provide a resin composition for laser processing capable of being adjusted to a desired color tone.
PTL 2 discloses a resin composition having excellent laser marking properties on a tag material in which resilience and soft feeling are required.
PTL 3 discloses a laser-markable thermoplastic resin composition which has conductivity and impact resistance and is excellent in color developability.
PTL 4 describes a polyamide-based conductive resin composition which is excellent in impact resistance and moldability and has good printing properties on laser marking.
PTL 5 describes a resin composition which is used for an application of forming a white marked area upon irradiation with a laser light.
PTL 6 describes a laser processing method of a carbon fiber-reinforced plastic and proposes a method of processing a composite material with an ultrashort pulse laser.